The present invention relates to a solid-shell or bowl type screw-conveyor centrifuge for the continuous separation of solid-liquid mixtures. The type of centrifuge contemplated by the present invention has a rotating screw-conveyor arranged within a cylindrically and/or conically fashioned shell or bowl, which shell is also rotating at a different velocity than the screw to affect centrifugal forces on the material. The radial dimensions of the screw helix are adapted to the design of the shell or bowl to facilitate conveying operations. The solid-liquid material mixture to be separated is fed at the beginning of the screw conveyor path into a separating chamber formed between the screw hub and the bowl. At least one discharge opening for the solid proportion of the material to be separated is provided adjacent the end of the screw conveyor path. Also, at least one liquid discharge conduit for the liquid proportion of the material terminates into the separating chamber at a liquid pick-up or receiving point which receiving point is at a distance from the beginning of the screw conveyor path as seen in the conveying direction.
It has been contemplated to withdraw the liquid proportion from the separating chamber at the receiving point with the aid of a peeling or paring element. In these arrangements, the peeling element is disposed in or on the screw body, which screw body is correspondingly radially enlarged at the receiving point and is provided with perforations. Thus, the screw body, at the receiving point, dips relatively greatly into the separating chamber and thereby considerably narrows the effective conveying passage for the solids. Also, with this type of arrangement, relatively strong eddies are produced in the separating chamber due to the protruding enlargement in the screw body. A further disadvantage with this arrangement of the peeling element within the screw at the receiving point is the required complex construction and consequent high costs.
The present invention contemplates the provision of a centrifuge of the general type mentioned in the foregoing which overcomes the above discussed disadvantages. The arrangement of the present invention is improved and/or simplified with respect to both its function and its constructional arrangement.
The present invention contemplates overcoming the above discussed disadvantages by providing a drain conduit arrangement extending from the receiving point along the screw hub to a liquid proportion drain chamber or zone of the bowl or shell. The drain chamber contemplated by the present invention has at least one drain port leading to the outside of the conveyor shell structure and is separated from the separating chamber. This drain conduit arrangement makes it possible to discharge the liquid proportion without a peeling device, whereby the troublesome widening of the screw hub structure at the receiving point and the disadvantages connected therewith are avoided. Also, screw conveyor of the construction according to the present invention can be of a very simple structure.
In a preferred embodiment contemplated by the present invention, the material to be separated is fed to the screw hub through a hollow chamber which communicates with the beginning of the screw conveyor path. A sealing disk or gasket is provided adjacent the beginning of the screw conveyor path which disk is penetrated by the drain conduit. This sealing disk extends from the screw hub radially outwardly closely to the inner wall of the bowl. Portions of solids which accumulate in the transitional zone between the sealing disk and the bowl assist in sealing the separating chamber from the drain chamber. With this arrangment, a particularly simple separation is attained between the separating chamber and the drain chamber. This preferred embodiment also exhibits constructionally especially simple structures for the feed of the material to be separated into the hollow chamber of the screw hub and for the discharge of the liquid proportion from the drain chamber.
The drain conduit arrangements contemplated for some preferred embodiments of the present invention may utilize pipes, or troughs, which extend from the screw hub in closely adjacent disposition or spaced-apart in parallel relation to one another. The pipes or troughs can be various cross-sectional shapes, for example of a rectangular configuration. In one preferred embodiment, only two mutually opposed pipes or troughs are employed. The pipes or troughs can freely end in the screw flight range from which the purified liquid is to be discharged or withdrawn. However, it is also contemplated by the present invention to provide sealable openings in each screw flight in order to be able to withdraw the purified liquid at various points, depending on the material being centrifuged. The present invention also contemplates using pipes or troughs of varying longitudinal dimension to effect withdrawal of the liquid at various points. In some particularly preferred embodiments of the invention, the pipes or troughs are accessible through drain bores in the lid or and of the bowl or shell. With this last-mentioned arrangement, it is possible to utilize pipes or troughs of varying lengths selectively, and to reduce or enlarge the cross section of the pipes by the insertion of plastic or metal strips for the purpose of changing the flow rate of the purified liquid. This arrangement makes it possible to readily remove any possible residual sedimentation from the pipes and/or troughs by removing the pipes or troughs and cleaning same.
In another preferred embodiment of the present invention, the pipes and/or troughs are disposed to be adjustable with respect to their radial distance from the longitudinal rotational axis of the screw. This radial adjustability feature makes it possible to maintain the immersion depth of the pipes and/or troughs at the optimum position suitable for the treatment of each of various solid-liquid materials to be separated. Furthermore, liquids of different densities can be withdrawn with this arrangement. In this connection, it is to be noted that it is merely necessary to seal the point of penetration of the pipes and/or troughs through the sealing disk adjacent the drain chamber. Sealing devices are unnecessary in the passages through the screw helix that are located between the sealing disk and the receiving point.
Further, particularly interesting embodiments of the invention are obtained by utilizing, in a double-flight or multi-flight screw construction, part of the channels, at least one, as conveyor channels, whereas the remaining part of the channels, at least one, serves as the drain conduit. The channels serving as conveyor channels are communicated with the feed of the material to be separated while the channels serving as drain conduit channels are communicated with the drain chamber. The conveyor channels and the drain channels are in communication with one another at the receiving point. This double usage of the channels between multiple-flight screw helix blades is workable as the gap between the individual screw flights and the inner wall of the bowl or shell is practically sealed off by solids after shortly after the material mixture is introduced. This sealing action can be improved according to the present invention by providing longitudinal strips within the bowl, between which a solids film is retained. Accordingly, the drain channel or channels are separated from the conveyor channel or channels except for the connection at the receiving point. Basically, the material to be separated can be fed into the conveyor channel or channels from the wider end face of the bowl in the peripheral zone thereof. The liquid proportion obtained in the same end of the bowl in the drain channel or channels is withdrawn, for example with the aid of a peeling element, and removed through the screw hub. However, in a preferred embodiment, here again a sealing disk is utilized, as described hereinabove. Under this prerequisite, a double-flight screw equipped in accordance with the invention operates as follows:
The material to be separated is introduced into the separating chamber through a cavity in the screw hub and through corresponding perforations in the casing of the screw hub in the initial zone of the screw conveyor path and fed into one of the two screw channels sealed at the front face by the sealing disk. The material to be separated travels along this screw channel in the direction of the smaller bowl diameter. At the receiving point which is suitably provided at the point where the maximum clarification of the material present in the conveyor channel has been attained, the liquid proportion flows through the connection provided at that point between the screw conveyor channel into the drain screw channel, which drain screw channel is not charged with material to be separated. The connection can be effected in the form of simple openings disposed in the screw flight between the conveyor channel and the drain channel and arranged suitably approximately at the height of the liquid level of the bowl. The liquid proportion transferred through the openings into the drain channel flows therein along the screw thread back to the larger diameter of the bowl. The drain channel penetrates the sealing disk, preferably likewise at the height of the liquid level, so that the liquid proportion can flow off via the weir disk or via a peeling element or the like.
A special advantage in removing the liquid proportion according to the present invention by means of one or more separate screw channels resides in that, in these drain channels, a further additional sedimentation of finer solids can definitely take place without these finer solids being able to clog the drain conduit constituted by the drain channel. Not only does clogging not take place in the drain channels, the entire drain channel is available for a further clarification of the liquid proportion, since the thus-sedimented finer solids are seized by the screw and are conveyed in the direction of the smaller bowl diameter. Therefore, in an especially advantageous embodiment, the screw helix is provided with an interruption between the conveyor channel and the drain channel, which interruption is arranged at least in the zone of the screw helix facing the inner wall of the bowl. This interruption can form the connection between the conveyor channel and the drain channel by itself or additionally to other openings. Preferably, the interruption is provided in the initial zone of the bowl portion wherein the fine, sedimented solids have not yet been removed from the liquid. Since these find solids cause more or less great difficulties during their conveyance from the liquid level, the screw helix is suitably interrupted in such a manner that the fine solids are placed upstream of the coarser solids in the conveyor channel of the screw and can thus be more readily transported from the liquid zone into the dry zone.
In case of triple-flight screws, it is possible according to the present invention, to fashion two screw channels as conveyor channels and one screw channel as the drain channel. Also the reverse is possible. If, quite generally, the screw has more than two channels, for example n channels, then a number of 1 to n - 1 channels can be provided as conveyor channels and in each case the residual number can be provided as drain channels. The particular distribution of the drain and conveyor channels contemplated by the present invention will be extensively dependent on the consistency of the material to be separated. Also, the present invention contemplates making a screw channel serving as the drain channel narrower than a screw channel serving as the conveyor channel, in order to thereby make a larger clarifying volume available for the conveyor channel or channels.
The present invention also contemplates constructing the screw in such a manner that the drain channel is extended only up to the receiving point, while the conveyor channel is then further extended as a single-flight screw to the narrow end of the bowl. This arrangement has the advantage that, at the point where the solid substance is transferred from the liquid zone into the dry zone, the screw which is single-flight in this region can be provided with a flatter pitch, which flatter pitch improves the conveyance of particularly slurry-like or sludge-like solids. the present invention also contemplates employing normal, double - or multi-flight screws, with the corresponding openings or screw flight interruptions being provided at the receiving point and the drain channel or channels extended through the sealing disk. The present invention also contemplates arrangements with double-flight screws wherein an additional, narrow screw drain channel is provided, extending between the two screw channels.
The above-discussed and other objects, features and advantages of the present invention will become more apparent from the following detailed description thereof, when taken in connection with the accompanying drawings, which show, for the purposes of illustration only, several embodiments in accordance with the present invention.